Method of producing spherical oxide powder and apparatus for producing spherical powder, composite dielectric material, and substrate and process for poducing substrate

ABSTRACT

The present invention provides a production method of spherical oxide powder which includes a feeding step in which a granular powder composed of an oxide composition is fed into a combustion flame together with a carrier gas; a melting step in which said fed granular powder is melted in said combustion flame to obtain a melt; and a solidifying step in which said melt is solidified by being moved and placed outside said combustion flame.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a production method of sphericaloxide powder and a production apparatus of spherical powder, and acomposite dielectric material suitable for use in the high frequencyregion, a substrate and a production method of the substrate.

[0003] 2. Background Art

[0004] A fine oxide powder can be obtained by mixing materials, dryingthe mixture obtained and subsequently calcinating the dried mixture, andthen pulverizing the calcinated mixture with a pulverizing machine suchas a ball mill, or the like.

[0005] Such oxide powders are used as powders of single material for thecases of dielectric materials and magnetic materials, and some othertimes used as pastes mixed with an organic vehicle and as compositematerials combined with a resin material. An oxide powder which is usedas a paste or a composite material is required to have dispersionproperties and packing properties for an organic vehicle and a resinmaterial (hereinafter, a generic term “a resin material” will be used)Here, the dispersion properties mean the degree of dispersion of anoxide powder in a resin material, and it is preferable that an oxidepowder is dispersed in a resin material with a higher degree ofuniformity. In addition, the packing properties signify the quantity ofan oxide powder filling in a resin material, and it is preferable that alarger quantity of an oxide powder fills in a resin material. A factorfor an oxide powder to acquire the dispersion properties and packingproperties for resin materials is the particle size of the powder. Inaddition to the above described method, a precipitation method canproduce oxide powders in which method oxide powders are produced fromthe liquid phase, but the particle size of the oxide powders thusproduced is too fine to acquire the dispersion properties and packingproperties for resin materials. On the other hand, an oxide powderobtained by pulverizing as mentioned above, and accordingly the particleshape is so irregular that the dispersion properties and packingproperties for resin materials cannot be acquired. In other words,another factor for an oxide powder to acquire the dispersion propertiesand packing properties for resin materials is the particle shape.Incidentally, in the present specification, a powder signifies anensemble of particles; when the substance concerned is judged to beappropriately referred to as a powder as being an ensemble of particles,the substance will be referred to as “powder”, and when the substanceconcerned is judged to be appropriately referred to as particles asbeing units constituting a powder, the substance will be referred to as“particles.” Since the powder and the particle share the commonfundamental unit, needles to say there are sometimes no substantialdifferences between the powder and the particle. Accordingly, there aresome cases where either the expression of “powder” or the expression of“particles” can be used.

[0006] For the purpose of acquiring the dispersion properties andpacking properties for resin material, the particles constituting apowder are preferably spherical, and more preferably nearly of the truesphere. In addition, it is preferable that the particle size is uniform,that is, the width of the particle size distribution is small.

[0007] A variety of production methods of spherical oxide powders havehitherto been proposed, for example, as in Japanese Patent Laid-Open No.2000-107585, Japanese Patent Laid-Open No. 8-48560, and Japanese PatentLaid-Open No. 5-105502.

[0008] Japanese Patent Laid-Open No. 2000-107585 discloses a productionmethod of spherical oxide powder in which a slurry is prepared bykneading an oxide powder with an appropriate binder, and the slurry isdripped on a high temperature heating body.

[0009] In addition, Japanese Patent Laid-Open No. 8-48560 discloses aproduction method of fine molded oxide spheres in which the oxide powdergranules obtained by the spray granulation method are used as nuclei, inproducing the fine molded oxide spheres which are produced by moldingthe oxide powder obtained by the stirring granulation method.

[0010] Furthermore, Japanese Patent Laid-Open No. 5-105502 discloses aninjection molded material which contains the oxide spherical powderhaving the mean particle size of 7 μm or below and a binder resin.

[0011] The above described production method of Japanese PatentLaid-Open No. 2000-107585 is, however, not suitable for the compositeformation with resin materials, since the obtained powder is surelyspherical, but the particle size is as large as 0.3 to 1.2 mm (300 to1200 μm).

[0012] The method disclosed in Japanese Patent Laid-Open No. 8-48560aims at obtaining powders having the size of 0.02 to 0.4 mm (20 to 400μm) not suitable for composite formation with resin materials.

[0013] Japanese Patent Laid-Open No. 5-105502 discloses an injectionmolded material containing an oxide spherical powder having the meanparticle size of 7 μm or below and a binder resin, but does not discloseany specific techniques of obtaining spherical oxide powders.

[0014] As stated above, conventionally it has been difficult to obtainthose spherical oxide powders having particle size and its distribution,which are suitable for composite formation with resin materials. Inparticular, no technique has been found for obtaining multicomponentoxides such as a composite oxide.

[0015] As a method of obtaining spherical oxide powders other than thosedescribed above, the plasma-flame method can be considered to be used.The method using plasma flame consumes an electric power of severalhundred kW in addition to the consumption of a large volume of expensiveargon gas as carrier gas, and hence there is a problem that the cost ishigh. Accordingly, the method using plasma flame is still in a positionfar way from the application to mass production.

[0016] Accordingly, the present invention provides a method capable ofproducing, without raising the cost, an oxide powder which has theparticle size suitable for composite formation with resin materials, andis excellent in the dispersion properties and packing properties forresin material. Furthermore, the subject of the present invention is toprovide an apparatus suitable for use in such a method of producing aspherical oxide powder. Another subject of the present invention is toprovide, by using such spherical oxide powders, a composite dielectricmaterial having a high dielectric constant ε and a low tan δ, and beingsuitable for use in the high frequency GHz band, and a substrateproduced by using the composite dielectric material of the presentinvention.

DISCLOSURE OF THE INVENTION

[0017] The present inventors have investigated the production ofspherical oxide powders by melting the materials by use of a combustionflame. The production method of spherical powder using a combustionflame is disclosed, for example, in National Publication ofInternational Patent Application No. 1999-514963, Japanese PatentLaid-Open No. 2001-97712, and Japanese Patent Laid-Open No. 2001-19425.In these prior arts, the materials are irregular shape powders, inparticular, typically powders obtained by pulverization.

[0018] An irregular shape powder produced by pulverization, however, hasa large width of particle size distribution. When such a powder having alarge width of particle size distribution is fed into a combustionflame, that is, a powder as a mixture of particles with large particlesizes and particles with small particle sizes is fed into a combustionflame, the following problem occurs. Namely, Particles with largeparticle sizes sometimes cannot be spheroidized when fed into acombustion flame owing to incomplete melting. For the purpose of meltingthe particles with large particle sizes, it is easily anticipated thatthe elevation of the combustion flame temperature or the elongation ofthe time of staying in the combustion flame will be effective. In such acase, however, there occurs an adverse effect that the particles withsmall particle sizes are evaporated.

[0019] In the present invention, the form of a powder to be fed into acombustion flame is recommended to be granular. More specifically, whena fine powder obtained by a liquid phase method such as theprecipitation method or the like is processed by the spray granulationmethod, in which the spray-drier is a representative apparatus, theobtained powder is granular and can be controlled to have a small widthof particle size distribution. Furthermore, by suitably setting thecondition for the spray granulation method, the particle size of thegranular powder can be nearly arbitrarily controlled. Consequently, whena granular powder thus obtained is fed into a combustion flame, theparticle size distribution of the powder finally obtained can be madenarrower.

[0020] The production method of spherical oxide powder of the presentinvention is based on the above described knowledge. That is, thepresent invention is characterized in that the method comprises afeeding step in which a granular powder composed of an oxide compositionis fed into a combustion flame together with a carrier gas, a meltingstep in which the fed granular powder is melted in the combustion flameto obtain a melt, and a solidifying step in which the melt is moved andplaced outside the combustion flame to be solidified.

[0021] In the present invention, for example, when the barium titanate(BaTiO₃) powder is finally obtained, the granular powder can be composedof a mixture containing the TiO₂ particles and BaCO₃ particles, inaddition to the case where the granular powder is composed of only theBaTiO₃ particles. Namely, there are two cases for the preparation of agranular powder in the present invention: in one case, the granularpowder is composed of the compound identical with the spherical oxidepowder obtained through the solidifying process, and in the other case,the granular powder is composed of plural kinds of particles. The caseswhere the granular powder is composed of plural kinds of particlesincludes the case where the granular powder is composed of the particlesof compounds and elemental simple substances, in addition to the casewhere the granular powder is composed of the particles of plural kindsof compounds. The state of the granular powder includes the two states;one is the state of dryness and the other is the state as a mixture witha slurry.

[0022] A specific target of the present invention is the dielectricmaterial composed of composite oxides. By the way, a spherical oxidepowder obtained in the present invention preferably has a mean particlesize of 1 to 10 μm and a sphericity of 0.9 or above. More preferablemean particle size is 1 to 6 μm and more preferable sphericity is 0.95or above.

[0023] In the present invention, as described above, a granular powdercomposed of plural different kinds of particles can be fed into acombustion flame. In this case, while the granular powder is melted inthe combustion flame, the different kinds of particles, typicallyparticles of different compounds react with each other, and finally thedesired oxide powder can be formed. This process is an efficient processin which the spheroidization can be achieved. Accordingly, the presentinvention provides a production method of spherical oxide powder whichmethod is characterized in that producing a powder, in which two or morethan two kinds of particles, capable of finally constituting a desiredoxide powder by a thermal reaction, are aggregated in a state of beingin contact with each other, and making said powder produced to stay in acombustion flame for a prescribed period of time.

[0024] The present invention provides the following production apparatussuitable for the above described production methods of spherical oxidepowder. Namely, the production apparatus of spherical powder of thepresent invention is characterized in that the production apparatuscomprises a burner for generating a combustion flame, an in-processsubstance feeding means for feeding a in-process substance to saidcombustion flame, a chamber provided with an in-process substancetransiting region through which the in-process substance, heat treatedby the combustion flame, passes in a floating state, and a heating meansfor heating said in-process substance transiting region. The productionapparatus of the present invention is characterized in that a heatingmeans is provided to prevent the in-process substance, having beenstayed in the combustion flame for a prescribed period of time, fromabrupt decrease in temperature. The abrupt temperature decrease causesthe following problems. The heating device in the present invention isprovided with for the purpose of solving these problems.

[0025] (1) Formation of single crystal particles is difficult sincecrystals can not grow largely.

[0026] (2) A high temperature phase remains in a portion of a formedparticle.

[0027] (3) Abrupt cooling makes the texture during solidification toremain in the structure of a particle.

[0028] (4) In the formation of the composite particles having suchcomposite structures as core-shell structures and the like, the phaseseparation and the composition precipitation within the particles do notproceed to a sufficient extent owing to the abrupt cooling, and hence itis difficult to obtain the desired structure.

[0029] The heating means of the production apparatus according to thepresent invention can comprise a plurality of heating parts. In thiscase, when the temperatures of the plurality of heating parts areadjusted to be different from each other so as to decrease on goingalong the transit direction of the in-process substance, the in-processsubstance can be cooled slowly in the in-process substance transitingregion. Additionally, the heating means is preferably equipped with agas flow controlling means for controlling the gas flow in thein-process substance transiting region. Furthermore, when the heatingmeans is equipped with the gas flow controlling means for controllingthe gas flow in the in-process substance transiting region, the movementof the in-process substance in the in-process substance transitingregion can be controlled. As for the gas flow controlling means, such ameans that is provided with a gas feeding opening, capable of feedingthe gas along an arbitrary direction, is applicable.

[0030] By the way, recently with the rapid increase of communicationinformation, reduction in size and weight, and speedup of communicationappliances are eagerly demanded. Particularly, the frequency band of theradio waves, for use in the cellular mobile communication such as carphones and digital cellular phones, and in the satellite communicationfalls in a high frequency band ranging from the megahertz band to thegigahertz band (hereinafter, referred to as “GHz band”).

[0031] In the rapid development of the communication appliances beingused, downsizing and high density mounting have been attempted for thecases, substrates, and electronic elements. For the purpose of furtherpromoting the reduction in size and weight of the communicationappliances for the high frequency bands, the materials for thesubstrates and the like used in communication appliances are required tobe excellent (small in dielectric loss) in high frequency transmissionproperties in the GHz band.

[0032] The dielectric loss is proportional to the product of thefrequency, the dielectric constant ε of the substrate, and thedielectric dissipation factor (hereinafter, represented by tan δ).Accordingly, for the purpose of reducing the dielectric loss, it isnecessary to reduce the tan δ of the substrate. In addition, thewavelength of an electromagnetic wave is contracted in a substrate by afactor of 1/{square root}{square root over (ε)}, and hence the larger isthe dielectric constant ε, the substrate size can be made the smaller.

[0033] From the above, the circuit boards for the downsizedcommunication appliances, electronic appliances, and informationappliances used in a high frequency band are required to have suchmaterial properties that the dielectric constant ε is high and tan δ issmall.

[0034] As the materials used for such circuit boards, dielectricmaterials are used as inorganic materials, while fluororesins and thelike are used as organic materials. The substrates made of dielectricmaterials are excellent in the properties of dielectric constant ε andtan δ, but have drawbacks in dimension accuracy and machinability, andhave a problem that the dielectric substrates are so brittle that theyare easily chipped and cracked. On the other hand, the substrates madeof organic materials such as resins and the like have the advantages ofexcellent moldability and machinability, and small tan δ, but have aproblem that the dielectric constants ε are small. Accordingly,recently, for the purpose of obtaining substrates simultaneously havingboth advantages thereof, composite substrates have been proposed whichare formed as composite substances of organic materials and inorganicmaterials by mixing dielectric materials in resin materials (forexample, see Japanese Patent No. 2617639, etc.).

[0035] Accompanying the advent of such composite substrates, thosedielectric materials which are excellent in dispersion properties andpacking properties for resin material are demanded. As described above,there are two factors, particle size and particle shape, for acquiringdispersion properties and packing properties for resin material.

[0036] In the above-mentioned Japanese Patent No. 2617639, made aproposal wherein titanium oxide particles having a high dielectricconstant is selected as dielectric material, the surfaces of thetitanium oxide particles are provided with an inorganic coating composedof inorganic hydroxides and/or inorganic oxides, and the dispersionproperties for resin are acquired by dispersing the coated particles ina resin material.

[0037] A substrate made of the dielectric material described in JapanesePatent No. 2617639, however, has a problem that the tan δ in the highfrequency (particularly, 100 MHz or above) band is large. In view of thetendency that in future the frequency band in use be changing over tothe higher frequency bands, there is a demand for a composite dielectricmaterial which can acquire a high dielectric constant ε and a low tan δ,that is, a high Q value (here, Q is the reciprocal of tan δ, Q=1/tan δ).

[0038] According to the investigations made by the present inventors,the spherical dielectric powder obtained by the above describedproduction method of spherical oxide powder of the present invention isexcellent in the dispersion properties and packing properties for resinmaterial. Consequently, a composite dielectric material composed of thespherical dielectric powder and a resin material has been found to haveexcellent high frequency properties. In other words, the presentinvention provides a composite dielectric material characterized in thatthe composite dielectric material comprises a resin material and aspherical dielectric powder dispersed in the resin material whichdielectric powder has a particle sphericity of 0.82 to 1, and the ratiobetween the 10% diameter of the powder and the 90% diameter of thepowder is 30 or below. By making the particle sphericity to be 0.82 to 1so as close to that of the true sphere, the dispersion properties andpacking properties of the dielectric material for resin material areremarkably improved.

[0039] The dielectric powder in the present invention is preferablybased on the BaO—RO—TiO₂ materials (R: a rare earth element, RO: a rareearth oxide). In addition, in the present invention, when the totalcontent of a resin material and a dielectric powder is represented as100 vol %, and the content of the dielectric powder is 30 vol % or aboveand smaller than 70 vol %, a high dielectric constant ε and an excellentQ value can be obtained in GHz band.

[0040] As described above, the dielectric powder in the presentinvention, the ratio between the 10% diameter of the powder and 90%diameter thereof is 30 or below. Namely, the particle size distributionof the powder is narrow. In addition to this, by making the meanparticle size of the dielectric powder to fall within the range from 0.5to 10 μm, the dispersion properties and packing properties of thedielectric material for resin material can be further improved. As fordielectric powder in the present invention, a spherical oxide powdersubjected to a heat treatment for spheroidizing the dielectric powder,can be employed.

[0041] As the resin material in the present invention, the polyvinylbenzyl ether compounds are suitable. The polyvinyl benzyl ethercompounds have such excellent electric properties that the dielectricconstant ε is low and the Q value is high (ε=2.5, Q=260) as comparedwith other resin materials. Accordingly, when the polyvinyl benzyl ethercompounds are used as the resin materials in the present invention,composite dielectric materials excellent in dielectric properties can beobtained.

[0042] Any composite dielectric material of the present invention issmall in dielectric loss even at 2 GHz so that it exhibits a high Qvalue. Specifically, at 2 GHz, the composite dielectric material canhave a Q value higher than that of the resin material (Q=1/tan δ, tan δbeing the dielectric dissipation factor).

[0043] In addition, the present invention provides a substrate wherein adielectric powder is dispersed in a resin material, the ratio of betweenthe 10% diameter and the 90% diameter is 30 or below in the dielectricpowder, and the particle sphericity of the dielectric powder is 0.82to 1. In this connection, a substrate in the present invention signifiesa substrate which is a circuit board or a multi-layer board for use inmounting electric parts, or a substrate for use in packagingsemiconductors for the purpose of housing semiconductor elements. Acomposite dielectric material of the present invention uses such adielectric powder that is narrow in particle size distribution and highin sphericity, and hence its fluidity becomes high. Consequently, thecomposite dielectric material can be densely filled even in theperipheries of the patterns (pattern edges) formed on the substrate, andthus there can be obtained a substrate which is high in dielectricproperties and also high in strength. Furthermore, when the totalcontent of the resin material and the dielectric powder is representedas 100 vol %, and the content of the dielectric powder is made to be 30vol % or above and smaller than 70 vol %, a substrate having adielectric constant of 8 or above in a high frequency band of 2 GHz canbe obtained. In addition, a substrate having a Q value of 300 or abovecan also be obtained in 2 GHz.

[0044] As the resin material in a substrate of the present invention,the polyvinyl benzyl ether compounds are suitable. The polyvinyl benzylether compounds have excellent electric properties as described above.In addition to this, the polyvinyl benzyl ether compounds are excellentin heat resistance and in chemical resistance, and simultaneously arecharacterized in that the water absorption is very low, and moreover theadhesion properties with a variety of materials are excellent. Thus, byusing a polyvinyl benzyl ether compound as the resin material, there canbe obtained a substrate which is low in water absorption and excellentin heat resistance and in chemical resistance.

[0045] In addition, in a substrate of the present invention, thedielectric powder is preferably based on the BaO—RO—TiO₂ materials (R: arare earth element, RO: a rare earth oxide). In addition, the dielectricpowder can be a spherical oxide powder subjected to a heat treatment forspheroidizing the dielectric powder.

[0046] Furthermore, the present invention provides a production methodof a substrate suitable for use in the high frequency region. To be inmore detail, by using the granules composed of an oxide composition,there is obtained a spherical oxide powder in which the ratio betweenthe 10% diameter and the 90% diameter is 30 or below, the mean particlesize is 0.5 to 10 μm, and the particle sphericity is 0.82 to 1. Then,the spherical oxide powder and a resin material are mixed together toobtain a mixture, and subsequently the mixture is subjected to thecompressing to obtain a substrate. In this connection, when the totalcontent of the resin material and the spherical oxide powder isrepresented as 100 vol %, the content of the spherical oxide powder ispreferably 30 vol % or above and smaller than 70 vol %. Moreover, in thepresent invention, the spherical oxide powder is preferably a dielectricceramic powder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 is a sectional view showing an example of a productionapparatus of spherical powder;

[0048]FIG. 2 is a graph showing an example of a temperature variation ina powder in the case where the powder was processed by using theapparatus shown in FIG. 1;

[0049]FIG. 3 is a graph showing an example of a temperature variation ina powder in the case where the powder was processed by using aproduction apparatus provided with no such a heating region as in theproduction apparatus of the present invention;

[0050]FIG. 4 is a figure showing the results of the microscopicobservation of the sections in Samples 1 and 2 produced in Example 3;

[0051]FIG. 5 is a figure showing schematically the results of themicroscopic observation of the sections in Samples 1 and 2 produced inExample 3;

[0052]FIG. 6 is a table showing the dielectric constants ε and Q valuesof Samples 2 to 5 measured in Example 4;

[0053]FIG. 7 is a figure showing the chemical formula of the polyvinylbenzyl ether compounds; and

[0054]FIG. 8 is a table showing the specific combinations of R₁ and thelike in the compounds represented by formula (1) given in FIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

[0055] Description will be made below on the embodiment of the presentinvention.

[0056] The present invention relates to oxides. In the presentinvention, the oxide is a concept including composite oxides. Notlimiting the oxides to be applied, the present invention can be appliedwidely to the dielectric materials and magnetic materials, etc. wellknown in the art.

[0057] As the dielectric materials, for example, those oxides based onbarium titanate, lead titanate, strontium titianate, and titaniumdioxide can be listed. As the magnetic materials, for example, Mn—Znbased ferrites, Ni—Zn based ferrites, Mn—Mg—Zn based ferrites, Ni—Cu—Znbased ferrites, and the like can be listed. In addition, the presentinvention is applicable to such iron oxides as Fe₂O₃ and Fe₃O₄.

[0058] The present invention is characterized in that granular powdersare used as material powders. This is ascribed to the fact that thewidth of the particle size distribution, as described above, can be madenarrow at the step of obtaining granular powders. Furthermore, theparticle size can also be controlled.

[0059] As a typical method of obtaining granular powders, there is aspray granulation method which uses a spray nozzle. In the spraygranulation method, a slurry is prepared for the purpose of spraying thestarting material powder from the spray nozzle. The slurry can beobtained by adding a proper amount of the starting material powder to asolvent, and subsequently mixing by use of a mixing machine such as aball mill, attriter, or the like. Water can be used as solvent, however,in order to increase the dispersion properties of the starting material,a dispersant such as ammonium polyacrylate A-30SL manufactured by ToaGosei, Inc. is recommended to be added. A bonding agent for mechanicallybinding the starting material powders, such as PVA (polyvinyl alcohol),can also be added.

[0060] The slurry containing the material powder is sprayed by use of aspray nozzle, a revolving disc, or the like to form droplets. Here, thespray nozzle is a device for use in spraying the above mentioned slurryand a compressed gas, and there can be used a two-fluid nozzle or afour-fluid nozzle.

[0061] The slurry discharged from the spray nozzle together with thecompressed gas is converted to fine particles to form mist. The dropletsize in the mist can be controlled by the ratio between the slurry andthe compressed gas. By controlling the droplet size, the particle sizeof the granules finally obtained can be controlled. By supplying theheat for drying the moisture during the process where the slurry in amist state falls down freely, there can be obtained a powder from whichthe liquid component is dried and removed. The heat can be supplied bymaking the gas discharged from the spray nozzle to be a heated gas, orby feeding a heated gas into the mist atmosphere. For the purpose ofdrying, a gas heated to 100° C. or above can be used. The processes ofspraying and drying with the spray nozzle are performed in a prescribedchamber. A powder obtained by the spray granulation method using a spraynozzle is usually a granular powder. The particle size of the granularpowder, as described above, can be controlled by the ratio between theslurry and the compressed gas. Fine droplets can also be formed bymaking the droplets of the slurry to collide with each other.

[0062] The granular powder obtained as described above is fed into acombustion flame. The fed granular powder stays in the combustion flameduring a prescribed period of time. During that stay, the granularpowder undergoes a heat treatment. Specifically, the granular powder ismelted to form spherical particles. When the granular powder is composedof two or more than two kinds of particles, the particles react witheach other so as to finally form the desired oxide. The granular powderbeing fed into the combustion flame can be fed in a dry state, andadditionally it can also be fed in a wet state as a slurry containingthe granular powder.

[0063] As for the combustion gas for obtaining the combustion flame,there is no particular restrictions, and such gases well known in theart as LPG, hydrogen, acetylene, or the like can be used. In the presentinvention, it is necessary to control the oxidation degree of thecombustion flame, since oxides are processed in the present invention.For the purpose of controlling the oxidation degree, it is desired tosupply an appropriate amount of oxygen to the combustion gas. When. LPGis used as the combustion gas, the oxygen amount of five times thesupply amount of LPG is equivalent to the LPG amount, when acetylene isused as the combustion gas, the oxygen amount of 2.5 times the supplyamount of acetylene is equivalent to the acetylene amount, and whenhydrogen is used as the combustion gas, the oxygen amount of 0.5 timesthe supply amount of hydrogen is equivalent to the hydrogen amount. Byappropriately setting the supply amount of oxygen, with reference tothese oxygen amounts, the oxidation degree of the combustion flame canbe controlled. The flow rates of these combustion gases can beappropriately determined according to the size of the burner.

[0064] The temperature of a combustion flame is varied by the kind andamount of the combustion gas, the ratio thereof to the oxygen amount,the feeding rate of the granular powder, and the like. When LPG is usedas the combustion gas, the temperatures up to about 2100° C. can beobtained, and when acetylene is used as the combustion gas, thetemperatures up to about 2600° C. can be obtained.

[0065] As for the technique of feeding a granular powder into acombustion flame, there is no restrictions as far as the granular powderis allowed to enter the flame. In addition to this, the granular powderis preferably fed along the flame axis from the burner, in order toprolong the transit time of the granular powder passing through theflame. Accordingly, it is preferable that the granular powder isadjusted not to leak out of the flame before the granular powder reachesthe flame bottom.

[0066] The feeding of the granular powder is made by using such acarrier gas as oxygen or the like. In the present invention, a granularpowder having a satisfactory fluidity is used so that the conveyanceperformance by the carrier gas is excellent. Incidentally, in a casewhere a pulverized powder is delivered by using a carrier gas, theirregularity in shape and the wide width of the size distribution of apulverized powder cause a poor fluidity and an unsatisfactory conveyanceperformance. Needless to say, it is necessary to increase the amount ofa carrier gas for the purpose of increasing the feeding amount of agranular powder, and in the case where oxygen is used as the carriergas, it is necessary to reduce the amount of oxygen which is thesupporting gas, and to adjust the mixing ratio between the carrier gasand oxygen.

[0067]FIG. 1 is a sectional view showing an example of a productionapparatus suitable for the production method of spherical oxide powderof the present invention. The production apparatus 10 has a burner 11, achamber 25, a processed powder collecting means 40, and a gas dischargemeans 50.

[0068] The burner 11 has a water-cooled triple pipe structure, and theindividual regions are respectively connected to a granular powderfeeding pipe 12, a combustion gas feeding pipe 13, and an oxygen feedingpipe 14.

[0069] The chamber 25 is formed of a highly heat-resistant material suchas alumina, and a water-cooled jacket 21 holding the burner 11 isarranged at the top of a cylindrical body 26. The water-cooled jacket 21serves to adjust the generated combustion flame 15 and to prevent theproduction apparatus 10 from being damaged by the heat of the combustionflame 15. For the purpose of forming the heating region inside thecylindrical body 26, the first heating part 27 a, the second heatingpart 27 b, and the third heating part 27 c are arranged, successively ina downward-pointing manner, around the circumference of the cylindricalbody 26. For heating in the heating parts 27 a, 27 b, and 27 c, therecan be used a heating method well known in the art such as a heating byelectric power, a heating by burning gas, or a radio-frequency heating.Among these heating methods, the heating by electric power is preferablewhich can easily control the atmosphere inside the furnace.

[0070] Furthermore, a gas feeding path 29 connected to a gas feedingpipe 28 is arranged on the inside wall of the cylindrical body 26. Thegas feeding path 29 is equipped with gas feeding openings 30 a, 30 b,and 30 c for feeding the gas into the interior of the cylindrical body26. The bottom of the cylindrical body 26 is open and connected to acollecting vessel 41 for collecting the processed powder.

[0071] As for a gas discharge means 50, a cyclone 51, a filter device52, an air pump 53, a cleaning vessel 54, and a discharge pipe 55 areconnected to the side surface of the collecting vessel 41 for thepurpose of discharging the gas coming from the cylindrical body 26 in aharmless state. Here, in the present embodiment, the collecting vessel41 and the cyclone 51 constitute the processed powder collecting means40. As will be described later in detail, in the present embodiment, forthe purpose of increasing the time of the in-process powder 20 b stayingin the heating region, there is formed a circling gas flow w circlinginside the cylindrical body 26. Owing to the circling gas flow, 60 to90% of the in-processed powder 20 b is collected in the cyclone 51.

[0072] In a specific production method of spherical powder using theproduction apparatus 10, while feeding such a combustion gas as LPG orthe like from the combustion gas feeding pipe 13 of the burner 11 andoxygen from the oxygen feeding pipe 14, the combustion gas is ignited togenerate the combustion flame 15 directing downward.

[0073] Then, the granular powder 20 a (not shown in the figure) is fedfrom the granular powder feeding pipe 12 together with the carrier gas.The granular powder 20 a is fed into the combustion flame 15 formed withthe burner 11.

[0074] In the combustion flame 15, different portions have differenttemperatures as such that, for example, the temperatures of the centralportion and the peripheral portion are different. Accordingly, dependingon the kind of the granular powder 20 a and the processing type, thesize of the combustion flame 15 and the like are adjusted, andsimultaneously the feeding location of the granular powder 20 a is alsoadjusted. By the way, when the granular powder 20 a is melted by theheat of the combustion flame 15 to obtain the spherical processedpowder, the temperature of the combustion flame 15 is adjusted to be atemperature higher than the melting point of the granular powder 20 a.

[0075] The granular powder 20 a having thus stayed in the combustionflame 15 for a prescribed period of time is melted or modifiedchemically or physically by the heat of the combustion flame 15, andfalls down within the chamber 25. The granular powder 20 a having passedthrough the combustion flame 15 becomes the in-process powder 20 b.

[0076] Around the circumference of the chamber 25, the first heatingpart 27 a, the second heating part 27 b, and the third heating part 27 care arranged, successively in a downward-pointing manner from the burner11 to the collecting vessel 41, that is, along the traveling directionof the in-process powder. A heating region is formed inside the chamber25 by the first to third heating parts 27 a, 27 b, and 27 c.

[0077] In the heating region, the first heating part 27 a is set at atemperature lower than that of the location in the combustion flame 15through which location the granular powder 20 a passes. Furthermore, thesecond heating part 27 b is set at a temperature lower than that of thefirst heating part 27 a, and the third heating part 27 c is set at atemperature lower than that of the second heating part 27 b.Consequently, the internal temperature of the cylindrical body 26 ismade to decrease gradually from the first heating part 27 a to the thirdheating part 27 c.

[0078] While the in-process powder 20 b having passed through thecombustion flame 15 falls down, in a floating state, inside thecylindrical body 26 of the chamber 25, the in-process powder 20 b isexposed successively to the temperatures corresponding to the respectiveheating parts 27 a, 27 b, and 27 c, during the transit process throughthe first to the third heating parts 27 a, 27 b, and 27 c. Thus, thegranular powder 20 a, being in a high temperature melted state throughstaying in the combustion flame 15 for a prescribed period of time, isslowly cooled down without any abrupt decrease in temperature.

[0079]FIG. 2 is a graph showing an example of a temperature variation ina powder in a case where the powder was processed by using theproduction apparatus 10 of the present embodiment, while FIG. 3 is agraph showing an example of a temperature variation in a powder in acase where the powder was processed by using a production apparatuswhich was not provided with such a heating region as in the productionapparatus 10. In FIG. 2, the temperature of the in-process powder 20 b,heated to a high temperature by the combustion flame 15, is decreasedgradually in such a manner as to a temperature T1 in the first heatingpart 27 a, to a temperature T2 in the second heating part 27 b, and to atemperature T3 in the third heating part 27 c. For example, when thebarium titanate powder is processed, by arranging the first heating part27 a, the second heating part 27 b, and the third heating part 27 c asdescribed above, the temperature of the heating region can be maintainedin the range from 1200° C. or above and 1800° C. or below, andpreferably 1300° C. or above and 1600° C. or below, and hence the abrupttemperature decrease of the powder, following the movement thereof outof the combustion flame 15, can be avoided. On the contrary, whenprocessed without arranging the heating region, as FIG. 3 shows, anabrupt temperature decrease of the powder of 1000° C. or more (thetemperature difference of T0) occurs immediately after the movementthereof out of the combustion flame 15.

[0080] By arranging the transit region, in continuation with the burner11, in which region the temperature decreases gradually along thetraveling direction of the in-process powder 20 b, the abrupttemperature decrease can be prevented which occurs when the in-processpowder 20 b is not heated but is left as it is cooled.

[0081] The heating temperatures set for the respective heating parts 27a, 27 b, and 27 c are varied depending on the kind of the powder and theobject of the processing. The temperature set for the first heating part27 a is preferably in the neighborhood of the melting point of thegranular powder 20 a. The difference between the temperatures set forthe first heating part 27 a and the second heating part 27 b and thedifference between the temperatures set for the second heating part 27 band the third heating part 27 c are each preferably about 100 to 300° C.In the third heating part 27 c which is the last heating part in theheating region, the temperature is preferably set so as to avoid thequality alteration of the in-process powder 20 b. When the melting ofthe granular powder 20 a by the combustion flame 15 is aimed at, thetemperature of the first heating part 27 a is preferably set to atemperature in the neighborhood of the melting point of the granularpowder 20 a.

[0082] In the present embodiment, for the purpose of preventing theabrupt temperature decrease of the powder, it is preferable to have ameans which enables the powder to stay in the heating region for a longperiod of time. As a specific means for that purpose, a gas feedingmeans is arranged in the heating region of the production apparatus 10.The gas, being fed from a gas feeding pipe 28, passes through a gasfeeding path 29, and is ejected from respective gas feeding openings 30a, 30 b, and 30 c into the interior of the cylindrical body 26. Byejecting the gas in this way, the in-process powder 20 b is preventedfrom falling down in a straightway into the collecting vessel 41, sothat the in-process powder 20 b can be prevented from being abruptlycooled.

[0083] As shown in FIG. 1, for example, by inclining the gas ejectiondirection to the burner 11, a circling gas flow w circling inside thecylindrical body 26, along the direction intersecting the fallingdirection of the in-process powder 20 b, can be formed from the gas flowgenerated by the combustion flame 15 and the gas flows from the gasfeeding openings 30 a, 30 b, and 30 c. The in-process powder 20 b fallsdown into the processed powder collecting means 40 (collecting vessel 41and cyclone 51), while circling inside the cylindrical body 26 alongwith the circling gas flow w, and hence it takes time to fall down sothat the time of the in-process powder 20 b staying in the heatingregion is increased. Consequently, the in-process powder 20 b fallsdown, while being reliably cooled down in the heating region to thetemperatures of the respective heating parts 27 a, 27 b, and 27 c, andhence abrupt cooling down is prevented more reliably.

[0084] In such a way as above, the time of the in-process powder 20 bstaying in the heating region, achieved by feeding the gas into theinterior of the cylindrical body 26, is varied depending on thetemperature and the kind of the powder, and is preferably about 3 to 20sec, and more preferably about 5 to 15 sec. The gas used in thisprocessing can be selected by considering the reactivity with thein-process substance, etc. and it is for example N₂, O₂, Ar, air, or thelike.

[0085] As described above, the in-process powder 20 b, which has beenheated to a high temperature by staying in the combustion flame 15 for aprescribed period of time, is slowly cooled by passing through theheating region, without being abruptly cooled immediately after passingthrough the combustion flame 15. In this way, the in-process powder 20b, falling down inside the cylindrical body 26 to be cooled, is housedin the processed powder collecting means 40.

[0086] The processed powder 20 c, collected in the processed powdercollecting means 40, can be obtained as a processed powder havingexcellent properties to meet the object of the processing as being apowder composed of dense particles of high crystallinity, single crystalparticles, spherical particles (high sphericity particles), or the like.

[0087] Specifically, in the present embodiment, the powder having passedthrough the combustion flame 15 is made to pass through the heatingregion and thereby is made to be cooled slowly, that is, prevented frombeing abruptly cooled, so that particles having single crystal structurecan be easily obtained, without applying any post-processing (annealingprocessing, and the like).

[0088] A mean particle size of a powder obtained in the presentembodiment is about 0.1 to 50 μm, and particularly particles about 1 to10 μm in mean particle size can be obtained.

[0089] Furthermore, in the present embodiment, a powder having asphericity of 0.9 to 1 can be obtained, and moreover, a powder having asphericity of 0.95 to 1 can be obtained. When the sphericity is 0.9 orabove, a processed powder 20 c tends to be uniformly dispersed in othermaterials. Here, “spherical” includes polyhedrons very close to a truesphere, in addition to a true sphere with smooth surface. Specifically,there is also included a polyhedron particle, having an isotropicsymmetry and being enclosed by stable crystal surfaces, as representedby the Wulff model, and in addition having a sphericity close to 1. Eventhose particles which have fine concavities and convexities on thesurface or elliptic sections fall under the category of being“spherical” in the terminology of the present invention, when thesphericity falls within the range 0.9 to 1. Here, the “sphericity” isthe practical sphericity of Wadell, that is, the sphericity of aparticle is the ratio between the diameter of a circle which has thesame area as the projected area of the particle and the diameter of theminimum circle circumscribing the projected image of the particle.

[0090] Additionally, in the present embodiment, there can be easilyobtained a processed powder composed of particles having such acomposite particle structure as core-shell structure or the like,through appropriate selection of the material powder. In the presentembodiment, the in-process powder undergoes slow cooling, and hence thephase separation can occur within a particle. As an example of thoseparticles which have composite particle structure, there can be cited acore-shell structure particle obtained by processing a suspension ofsilver nitrate with silica particles dispersed therein.

[0091] In addition, there can be obtained products having excellentproperties, and materials and parts having special structure andfunctions, by using the processed powder 20 c in combination, asmixtures, or the like with other materials. In particular, as will bedescribed later, there can be obtained substrates, filters, and the likesuitable for use in the high frequency band.

[0092] In the above described production apparatus 10 shown in FIG. 1,the heating region is composed of the first to third heating parts, 27a, 27 b, and 27 c, but the heating region may be made up only by thefirst heating part 27 a, or alternatively may be constituted by morethan three heating parts. The number of the heating parts arranged isappropriately adjusted depending on the kind of the powder to beprocessed and the type of the purposed processing. The heating region isnot limited to that composed of the heating parts 27 a, 27 b, and 27 cas shown in FIG. 1, but for the heating region, there can be used suchan alternative heating unit as a unit in which a heated gas is injectedinto the interior of the cylindrical body 26, or the like, as far as itcan yield a temperature gradient making the temperature decrease alongthe falling direction of the in-process powder 20 b, that is, thedirection from the burner 11 to the processed powder collecting means40. Sometimes, a positive heating by use of the first to third heatingparts 27 a, 27 b, and 27 c is not performed, depending on the purposedtemperature gradient. Furthermore, through regulating the gas flowconditions in the cyclone 51, for example, the condition that thedirections of discharge from the cylindrical body 26 and the collectingvessel 41 are made to lie on a circumferential direction, and the like,the circling gas flow w is generated inside the cylindrical body 26without feeding the gas from the gas feeding openings 30 a, 30 b, and 30c, and thus the in-process powder 20 b can be prevented from beingabruptly cooled. Depending on the particle size distribution of aspherical powder, the processed powder 20 c in the collecting vessel 41and that in the cyclone 51 may be collected jointly by connecting thecollecting vessel 41 and the cyclone 51 with a pipe.

[0093] Now, description will be made on a case where a dielectric powderis selected as a material and the dielectric powder is dispersed in aresin to produce a composite dielectric material and a compositesubstrate suitable for use in the high frequency band.

[0094] As described above, since the dispersion properties and packingproperties for resin material are improved by making the particle shapeto be spherical, the dielectric powder is beforehand converted to aspherical powder by use of the production apparatus 10 shown in FIG. 1.Specifically, the dielectric powder is converted to a granular powder byuse of, for example, the above mentioned method (the spray granulationmethod), and is subsequently charged into the production apparatus 10.Then, the time of staying in the combustion flame 15 for the granularpowder and the like are adjusted so as to finally obtain a dielectricpowder having such a particle shape of sphericity 0.82 to 1.0 as isclose to a true sphere.

[0095] As a dielectric powder, those oxides based on barium titanate,lead titanate, strontium titianate, titanium dioxide, and the like, asdescribed above, can be used. Among these, the dielectric powders basedon barium titanate are preferable, and particularly, a paradielectricpowder based on BaO—RO—TiO₂ (R: a rare earth element, RO: a rare earthoxide) and exhibiting a tungsten bronze structure shows satisfactorydielectric properties in the high frequency band and hence ispreferable. Here, the rare earth element R refers to one or moreselected from the rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Er, Yb, and Lu) inclusive of Y. Among these, Nd is an abundantresource and relatively inexpensive, and hence it is preferable toselect Nd as main component for the rare earth element R.

[0096] When a dielectric powder based on BaO—RO—TiO₂ is used as adielectric powder, it is preferable that the blending composition issuch that BaO: 6.67 to 21.67 mol %, RO: 6.67 to 26.67 mol %, and TiO₂:61.66 to 76.66 mol %. In addition, the oxides of Bi, Mn, Zr, Cr, Co, Ta,Ge, Li, B, Mg, and the like may be appropriately added to thecomposition based on a BaO—RO—TiO₂ material. By adding Bi, thetemperature stability is improved, and simultaneously the dielectricconstant is also improved. In addition, by adding Mn, a high Q value canbe obtained. Furthermore, Zr, Cr, Co, Ta, Ge, Li, B, and Mg areeffective for improvement of the temperature stability.

[0097] When a composite dielectric material is obtained by mixing adielectric powder with a resin, the mean particle size of the dielectricpowder is adjusted to be 0.5 to 10 μm. When the mean particle size ofthe dielectric powder is smaller than 0.5 μm, it is difficult to obtainhigh dielectric properties, in particular, to obtain a dielectricconstant ε of 8 or above at 2 GHz. In addition, in a case where the meanparticle size of the dielectric powder is so smaller than 0.5 μm, thereoccurs such an inconvenience that the kneading with the resin is noteasy, and in addition, the handling becomes cumbersome as such that theparticles of the dielectric powder aggregate and accordingly anon-uniform mixture is formed, and the like.

[0098] On the other hand, when the mean particle size of the dielectricpowder exceeds 10 μm, the dielectric properties are satisfactory, butthere occurs a problem that the pattern formation becomes so tough thatit is difficult to obtain a thin and flat substrate. Consequently, themean particle size of the dielectric powder is made to be 0.5 to 10 μm.The preferable mean particle size of the dielectric powder is 1 to 6 μm,and the more preferable mean particle size is 3 to 5 μm. By making themean particle size of the dielectric powder 0.5 to 10 μm, it becomespossible to obtain a dielectric constant ε of 8 or above and a Q valueof 300 or above in a high frequency region of 2 GHz as well.

[0099] For the purpose of uniformly distributing the dielectric powderin the resin, it is effective to use the dielectric powder in which theparticle size distribution is narrow and the particle size is even. Aguideline for the particle size distribution and particle size is thatthe ratio between the 10% diameter and the 90% diameter is 30 or below,more preferably 20 or below, and further more preferably 15 or below.

[0100] By using the above described method and production apparatus 10,a dielectric powder with the sphericity of 0.82 to 1 can be obtained,and further a dielectric powder with the sphericity of 0.9 to 1 can beobtained. When a dielectric powder with the sphericity of 0.82 or aboveis used, it becomes easy to disperse the dielectric powder uniformly ina resin.

[0101] Here, the definition of “spherical” is as described above. In thepresent invention, when two or more than two particles are bonded byfusion, the individual particles are regarded as one particle for thecalculation of the sphericity. When there is a protrusion, a similartreatment is made.

[0102] In a composite dielectric material of the present invention, whenthe total content of a dielectric powder and a resin is represented as100 vol %, the content of the dielectric powder is 30 vol % or above andsmaller than 70 vol %. When the content of the dielectric powder issmaller than 30 vol % (the content of the resin exceeds 70 vol %), thedimension stability as a substrate is lost, and the dielectric constantε is decreased. Namely, no appreciable effect of containing dielectricpowder is found. On the other hand, when the content of the dielectricpowder is 70 vol % or above (the content of the resin is 30 vol % orbelow), the fluidity is extremely degraded when press molded, so that nodense molded product can be obtained. As a result, water invasion or thelike becomes easy, leading to degradation of the electric properties. Ascompared to the case where no dielectric powder is added, sometimes theQ value is largely decreased. Consequently, the content of thedielectric powder is set to be 30 vol % or above and smaller than 70 vol%. The preferable content of the dielectric powder is 40 to 65 vol %,and the more preferable content of the dielectric powder is 45 to 60 vol%. The optimal content of the dielectric powder varies according to thesubstrate pattern shape in such a way that the preferable content of thedielectric powder is about 35 to 45 vol % when the substrate patternshape is relatively fine.

[0103] Since as described above the dielectric powder of the presentinvention is spherical and the particle size distribution thereof isnarrow, the dispersion properties for resin are satisfactory even whenthe content of the dielectric powder is set to be 40 vol % or above, andfurthermore 50 vol % or above, and the dielectric powder can be filledin without degrading the fluidity of the resin material. Accordingly,when a dielectric powder of the present invention is mixed with a resinmaterial, and a substrate is produced by use of the mixture, thefilled-in amount of the dielectric powder is improved as compared withthe case where pulverized powder is used, and as a result a substratehaving a high dielectric constant ε can be obtained.

[0104] On the contrary, when there is used a non-spherical dielectricpowder such as a pulverized powder prepared by a conventional method,the fluidity of the resin material is deteriorated when the content ofthe dielectric powder in a substrate becomes about 40 vol %, and henceit is very difficult to make the content of the dielectric material in asubstrate 45 vol % or above. Granted that the content of the dielectricpowder in a substrate is permitted to be 45 vol % or above, it isdifficult for the dielectric powder to fill in the pattern edges and thelike in producing a substrate, and consequently there is obtained asubstrate having voids in some portions thereof and accordingly having alow strength.

[0105] Now, description will be made on the resin material in thecomposite dielectric material of the present invention. As the resinmaterial, organic polymer resins are preferable. The organic polymerresin is preferably a heat-resistant and low-dielectric-property polymermaterial which is a resin composite composed of one or more kinds ofresins with the weight-average absolute molecular weight of 1000 orabove, and in which the sum of the number of the carbon atoms and thenumber of the hydrogen atoms is 99% or above in ratio, and a part of theresin molecules or the whole resin molecules are chemically bonded toeach other. By using an organic polymer resin having such a constitutionas above, there can be obtained a composite dielectric material having ahigh dielectric constant ε and a high Q value in a high frequencyregion.

[0106] As described above, a heat-resistant and low-dielectric-propertypolymer material, made of a resin composite with the weight-averageabsolute molecular weight of 1000 or above, is used for the purpose ofattaining sufficient strength, adherence to metal, and heat resistance.With a weight-average absolute molecular weight smaller than 1000, thereoccur insufficiencies in mechanical properties and heat resistanceproperties.

[0107] The reason why the sum of the number of the carbon atoms and thenumber of the hydrogen atoms is made to be 99% or above in ratio is thatthe chemical bonds present in the polymer material are made to benon-polar bonds, and thereby it becomes easy to obtain a high Q value.On the other hand, the Q value becomes small, when the sum of the numberof the carbon atoms and the number of the hydrogen atoms is smaller than99% in ratio, in particular, when the number of the contained atomsforming polar molecules such as oxygen atoms and nitrogen atoms islarger than 1% in ratio.

[0108] The weight-average absolute molecular weight is particularlypreferably 3000 or above, and furthermore preferably 5000 or above. Inthis connection, there is no particular limit to the upper limit for theweight-average absolute molecular weight, but usually the upper limit isabout ten millions.

[0109] As specific examples of the above described organic polymerresins, there can be listed homopolymers and copolymers (hereinafter,sometimes referred to as (co)polymers) of non-polar α-olefins such aslow density polyethylene, ultra low density polyethylene, superultra lowdensity polyethylene, high density polyethylene, low molecular weightpolyethylene, ultra high molecular weight polyethylene,ethylene-propylene copolymers, polypropylene, polybutene,poly-4-methylpentene, and the like; (co)polymers of conjugated dienemonomers such as butadiene, isoprene, pentadienes, hexadienes,heptadienes, octadienes, phenylbutadienes, diphenylbutadienes, and thelike; and (co)polymers of carbon-ring containing vinyl monomers such asstyrene, nuclear substituted styrenes such as methylstyrenes,dimethylstyrenes, ethylstyrenes, isopropylstyrenes, chlorostyrenes,α-substituted styrenes such as α-methylstyrene, α-ethylstyrene,divinylbenzenes, vinylcyclohexanes, and the like.

[0110] As a resin used in the present invention, the polyvinyl benzylether compounds are particularly preferable. As the polyvinyl benzylether compounds, those compounds represented by formula (1) shown inFIG. 7 are preferable.

[0111] In formula (1), R₁ represents a methyl group or an ethyl group.R₂ represents a hydrogen atom or a hydrocarbon group having 1 to 10carbon atoms. The hydrocarbon groups represented by R₂ are an alkylgroup, an aralkyl group, an aryl group, and the like, each of whichgroups may contain substituents. The alkyl group is a methyl group, anethyl group, a propyl group, a butyl group, or the like, the aralkylgroup is a benzyl group or the like, and the aryl group is a phenylgroup or the like.

[0112] R₃ represents a hydrogen atom or a vinylbenzyl group, thehydrogen atom stems from a starting compound for synthesis of thecompound of formula (1), and the molar ratio of the hydrogen atom to thevinylbenzyl group is preferably 60:40 to 0:100, and more preferably40:60 to 0:100.

[0113] n is a number of 2 to 4.

[0114] By making the molar ratio of the hydrogen atom of R₃ to thevinylbenzyl group of R₃ to fall within the above ranges, the curingreaction when obtaining a dielectric compound can be proceeded to asufficient extent, and satisfactory dielectric properties can beobtained. On the contrary, when the unreacted compound in which R₃ is ahydrogen atom is increased in content, the curing reaction does notproceed to a sufficient extent, and no satisfactory dielectricproperties can be obtained.

[0115] Specific examples for the combination of R₁ and the like in thecompound represented by formula (1) are shown in FIG. 8, the combinationis not limited to these examples.

[0116] The compound represented by formula (1) is obtained by reacting apolyphenol with R₃═H in formula (1) and a vinylbenzyl halide. As for thedetails of the reaction, the descriptions in Japanese Patent Laid-OpenNo. 9-31006 can-be referred to.

[0117] The polyvinyl benzyl ether compounds of the present invention maybe used each alone or in combination of two or more kinds of compoundsthereof. A polyvinyl benzyl ether compound of the present invention maybe used alone in a polymerized form as a resin material, or may be usedas polymerized with other monomers, or furthermore can be used incombination with other resins.

[0118] As polymerizable monomers, there can be listed, for example,styrene, vinyltoluenes, divinylbenzenes, divinylbenzyl ethers, allylphenol, allyloxy benzenes, diallyl phthalates, acrylic acid esters,methacrylic acid esters, vinyl pyrrolidones, and the like. As for theblending ratios for these monomers, the blending ratio is about 2 to 50mass % to a polyvinyl benzyl ether compound.

[0119] As resins usable in combination, there are thermosetting resinssuch as vinyl ester resins, unsaturated polyester resins, maleimideresins, polycyanate resins of polyphenols, epoxy resins, phenol resins,vinylbenzyl compounds and the like; and thermoplastic resins such aspolyether imide resins, polyether sulfones, polyacetals, resins based ondicyclo pentadienes. As for the blending ratios for these resins, theblending ratio is about 5 to 90 mass % to a polyvinyl benzyl ethercompound of the present invention. Among these resins, preferable resinis at least one selected from a group consisting of vinyl ester resins,unsaturated polyester resins, maleimide ester resins, polycyanate resinsof polyphenols, epoxy resins, and the mixtures of these resins.

[0120] The polymerization and curing of either the polyvinyl benzylether compounds themselves of the present invention, or thethermosetting resin composites containing these compounds and othermonomers or thermosetting resins, can be performed by a method wellknown in the art. The curing can be performed either in the presence orin the absence of a curing agent. As a curing agent, there can be used aradical polymerization initiator well known in the art such as benzoylperoxide, methyl ethyl ketone peroxide, dicumyl peroxide, t-butylperbenzoate, or the like. The usage amount of an initiator is 0 to 10mass parts to 100 mass parts of a polyvinyl benzyl ether compound.

[0121] The curing temperature is varied depending on whether a curingagent is used and according to the type of the curing agent used, and itis 20 to 250° C., and preferably 50 to 250° C. for a sufficient curing.

[0122] For curing regulation, hydroquinone, benzoquinone, copper salts,and the like may be blended.

[0123] A reinforcing material can be added to a resin of the presentinvention. A reinforcing material is effective in improving themechanical strength and the dimension stability, and hence usually aprescribed amount of a reinforcing material is added to the resin inproducing a circuit board.

[0124] As the reinforcing materials, there can be listed fibrousreinforcing materials or plate-like or granular non-fibrous reinforcingmaterials. Among the fibrous reinforcing materials, here can be listedinorganic fibers such as glass fiber, alumina fiber, aluminum boratefiber, ceramics fiber, silicon carbide fiber, asbestos fiber, gypsumfiber, brass fiber, stainless fiber, steel fiber, metal fibers,magnesium borate whisker or fiber thereof, potassium titanate whisher orfiber, zinc oxide whisker, boron whisker fiber, and the like; and carbonfiber, aromatic polyamide fibers, aramide fibers, polyimide fibers, andthe like. When a fibrous reinforcing material is used, there can beadopted a so-called impregnation method described in Japanese PatentLaid-Open No. 2001-187831. Namely, the point is that a fibrousreinforcing material molded in a sheet shape is immersed in a coatingvessel in which the dielectric powder and the resin are mixed to preparea slurry.

[0125] As the non-fibrous reinforcing materials, there can be listedneedle-like, plate-like, or granular reinforcing materials which aresilicates such as wollastonite, sericite, kaolin, mica, clay, bentonite,asbestos, talc, alumina silicate, pyrophyllite, montmorillonite, and thelike; molybdenum disulfide, alumina, silicon chloride, zirconium oxide,iron oxides; carbonates such as calcium carbonate, magnesium carbonate,dolomite, and the like; sulfates such as calcium sulfate, bariumsulfate, and the like; calcium polyphosphate, graphite, glass bead,glass microballoon, glass flake, boron nitride, silicon carbide, andsilica. These materials may be hollow. When a non-fibrous reinforcingmaterial is used, it only has to be added to a resin.

[0126] These reinforcing materials may be used each alone, or can beused in combination with two or more than two kinds of materialsthereof, and if need be, can be applied a pretreatment with couplingagents based on silane or titanium. A particularly preferablereinforcing material is glass fiber. As for the type of glass fiber,there is no particular limitation to it, and there can be used thosewhich are generally used in reinforcing resins. The glass fiber to beused can be selected from, for example, chopped strands of long fibertype and short fiber type, chopped strand mat, continuous long fibermat, cloth-like glass such as fabric, knit fabric, or the like, andmilled fiber.

[0127] The content of a reinforcing material in a composite dielectricmaterial preferably falls in the range from 10 to 30 wt %, and morepreferably from 15 to 25 wt %.

[0128] A composite dielectric material of the present invention ispreferably produced by the following method.

[0129] At the beginning, a dielectric powder having spherical particleshape is obtained according to the above described method. Then, thedielectric powder having spherical particle shape and a resin are mixedtogether in prescribed amounts. The mixing can be performed, forexample, by a dry mixing method, but it is preferable that the mixing isfully performed in an organic solvent such as toluene, xylene, or thelike by use of a ball mill, a stirring machine, or the like.

[0130] The slurry thus obtained is dried at 90 to 120° C. to obtain thechunks composed of the dielectric powder and the resin. The chunks arepulverized to obtain the mixed powder composed of the dielectric powderand the resin. The process from slurry to mixed powder preferably uses aproduction apparatus of granular powder such as a spray drier, or thelike.

[0131] The mean particle size of the mixed powder is recommended to beabout 50 to 1000 μm.

[0132] Then, the mixed powder undergoes press molding at 100 to 150° C.into a desired shape, and the molded substance is cured at 100 to 200°C. for 30 to 480 min. In the course of this curing process, areinforcing material described above is allowed to be involved.

[0133] As for the composite dielectric material of the presentinvention, as described above, a dielectric powder is preferably mixedin before the polymerization or the curing of a resin such as apolyvinyl benzyl ether compound, or the like, but it may be mixed inafter the polymerization or the curing as the case may be. It is notpreferable, however, that the dielectric powder is mixed in aftercompletion of curing.

[0134] A composite dielectric material of the present invention can beused in a variety of shapes such as film, a molded body in bulk form orin a prescribed shape, a film lamination, or the like. Accordingly, itcan be used for a variety of substrates for use in electronic equipmentsand electronic parts (resonators, filters, condensers, inductors,antennas, and the like) for use in the high frequency band; for filters(for example, a C filter which is a multilayer substrate) and resonators(for example, a triplate resonator) as chip parts; for supporting basesfor dielectric resonators or the like; furthermore, for housings for avariety of substrates or electronic parts (for example, an antenna rodhousing); for casings, and for electronic parts and housings or casingsthereof, or the like. As for the substrates, they are expected to bealternative to conventional glass fabric based eopoxy resin substrates,and specifically examples include on-board substrates for use inmounting parts, copper-clad laminates, metal based/metal coresubstrates, and the like. Furthermore, the substrates can be used forcircuit integrated boards and antenna substrates (patch antenna and thelike). In addition, they can be used for on-board substrates for CPU.

[0135] Incidentally, in formation of an electrode, a compositedielectric powder is placed between metal foil sheets of copper or thelike, and cured while pressing; or a foil sheet of copper or the like isattached to one side surface of a molded body of the compositedielectric powder, or two metal foil sheets on both side surfaces,before completion of curing, and the curing can be performed whilepressing. In addition, an electrode may be formed as follows: atemporary curing is performed after attaching metal foil sheet bypressing, and subsequently a separate curing is performed by heattreatment; and the molded substance is cured, and then undergoes themetal evaporation, metal sputtering, electrolytic-less plating, orcoating with (resin) electrode or the like.

[0136] A composite dielectric material of the present invention and aboard using thereof can be used suitably in the GHz band, and can have adielectric constant E of 8 or above and a Q value of 300 or above in thecase of the 2 GHz band.

[0137] With reference to the following specific examples, detaileddescription will be made below on the present invention.

EXAMPLE 1

[0138] To the barium titanate (BaTiO₃) particles with the mean particlesize of 0.8 μm obtained by a precipitation method, the spray granulationmethod was applied to yield a granular powder with the mean particlesize of 6.9 μm. The granular powder had a sphericity of 0.93 and a tapdensity of 2.3 g/cm³. In addition, the particle size distribution of thegranular powder was measured to give the 10% diameter of 1.48 μm and the90% diameter of 12.3 μm. Accordingly, the ratio between the 10% diameterand the 90% diameter of this granular powder is 8.3.

[0139] Incidentally, the 10% diameter means the particle size at whichsize point the cumulative curve becomes 10%, where the cumulative curveis obtained with the total volume of the measured powder taken to be100%. Similarly, the 90% diameter is the particle size at which sizepoint the cumulative curve becomes 90%. Accordingly, it is meant thatthe smaller is the difference between the 10% diameter and the 90%diameter, the narrower is the particle size distribution, while thelarger is the difference, the wider is the particle size distribution.

[0140] By using the apparatus shown in FIG. 1, the combustion flame 15was generated while feeding LPG from the combustion gas feeding pipe 13and oxygen from the oxygen feeding pipe 14, and the above describedgranular powder was fed together with oxygen as the carrier gas into thecombustion flame 15. Incidentally, the flow rates of oxygen and LPG forgenerating the combustion flame 15 were 10.0 l/min and 2.0 l/min,respectively. And the flow rate of oxygen as the carrier gas was 1.0l/min. For the obtained powder, the mean particle size was 6.6 μm, the10% diameter was 1.36 μm, and the 90% diameter was 10.2 μm. Accordingly,the ratio between the 10% diameter and the 90% diameter of the obtainedpowder is 7.5, a value smaller than 30. In addition, the tap density was2.9 g/cm³, and the sphericity of the particles constituting the powderreached 0.98.

EXAMPLE 2

[0141] The powder of titanium oxide (TiO₂) with the mean particle sizeof 0.1 μm and the powder of barium carbonate (BaCO₃) with the meanparticle size of 0.15 μm, both obtained by the precipitation method,were mixed with each other in the molar ratio of 1.0:1.0, and the slurrywith 50 wt % solid component was prepared. The slurry underwent thespray granulation, a granular powder with the mean particle size of 11.5μm was produced. The granular powder is a powder in which particles oftwo kinds of compounds are aggregated in a state of being in contactwith each other. In addition, for the granular powder, the sphericitywas 0.92, and the tap density was 2.0 g/cm³. The particle sizedistribution was measured to give the 10% diameter of 1.3 μm and the 90%diameter of 19.6 μm. Accordingly, the ratio between the 10% diameter andthe 90% diameter of the granular powder is 15.1.

[0142] Similarly to Example 1, in the apparatus shown in FIG. 1, thecombustion flame 15 was generated and the above described granularpowder was fed into the combustion flame 15 with oxygen as the carriergas. Incidentally, the flow rates of oxygen and LPG for generating thecombustion flame 15 were 12.0 l/min and 2.3 l/min, respectively. And theflow rate of oxygen as the carrier gas was 1.0 l/min.

[0143] For the obtained powder, the mean particle size was 8.6 μm, andaccording to the SEM (scanning electron microscope) observation, thegreater part of particles had flat and smooth surfaces, the overallsphericity reached 0.95. The particle size distribution was measured togive the 10% diameter of 1.1 μm and the 90% diameter of 11.3 μm (forthis powder, the ratio between the 10% diameter and the 90% diameter is10.3), and the tap density of 2.8 g/cm³. In addition, from theobservation of the constitution phase of the obtained spherical powderby X-ray diffraction, it was confirmed that barium titanate (BaTiO₃)constituted the main phase.

COMPARATIVE EXAMPLE 1

[0144] The powder of titanium oxide (TiO₂) with the mean particle sizeof 0.1 μm and the powder of barium carbonate (BaCO₃) with the meanparticle size of 0.15 μm, both obtained by the precipitation method,were mixed with each other in the molar ratio of 1.0:1.0, andsubsequently the calcination was performed at 1250° C. for 4 hours. Thecalcinated powder obtained was pulverized and a barium titanate (BaTiO₃)powder with the mean particle size of 7.2 μm was obtained.

[0145] The SEM observation of the powder confirmed that the powder wascomposed of particles with irregular shapes. The particle sizedistribution of the powder was measured to give the 10% diameter of 0.88μm and the 90% diameter of 22.4 μm (the ratio between the 10% diameterand the 90% diameter is 25.5).

[0146] Similarly to Example 1, in the apparatus shown in FIG. 1, thecombustion flame 15 was generated and the above described granularpowder was fed into the combustion flame 15 with oxygen as the carriergas. Incidentally, the flow rates of oxygen and LPG for generating thecombustion flame 15 were 10.0 l/min and 2.0 l/min, respectively. And theflow rate of oxygen as the carrier gas was 1.0 l/min.

[0147] The mean particle size of the obtained powder was 6.9 μm. Theparticle size distribution was measured to give the 10% diameter of 0.81μm and the 90% diameter of 18.4 μm (the ratio between the 10% diameterand the 90% diameter is 22.7). From the SEM observation, it wasconfirmed that a greater part of particles had flat and smooth surfaces.However, it was also confirmed that the particles with the particle sizeof 10 μm or above, which particles account for 30% of the wholeparticles, had still angular portions and the like, and did not becomespherical. For the powder obtained, the sphericity was 0.87 and the tapdensity was 2.3 g/cm³.

COMPARATIVE EXAMPLE 2

[0148] The powder of titanium oxide (TiO₂) with the mean particle sizeof 0.1 μm and the powder of barium carbonate (BaCO₃) with the meanparticle size of 0.15 μm were mixed with each other in the molar ratioof 1.0:1.0. Similarly to Example 1, in the apparatus shown in FIG. 1,the combustion flame 15 was generated and the above described granularpowder was fed into the combustion flame 15 with oxygen as the carriergas. Incidentally, the flow rates of oxygen and LPG for generating thecombustion flame 15 were 12.0 l/min and 2.3 l/min, respectively. And theflow rate of oxygen as the carrier gas was 1.0 l/min.

[0149] The mean particle size of the obtained powder was 0.9 μm.According to the results of the SEM observation, the particles had flatand smooth surfaces, and the sphericity reached 0.91. The constitutionphase of the obtained powder was observed by X-ray diffraction, and itwas confirmed that the particles were constituted by the mixturescomposed of a lot of substances such as TiO₂, BaO, BaTiO₃, Ba₂TiO₄,BaCO₃, and the like.

EXAMPLE 3

[0150] The material powders of Nd₂O₃, BaO, and TiO₂ were mixed togetherfor 10 min by use of a fluid granulation-drying apparatus (the product'sname: Pulvis Mini-bed GA-22 manufactured by Yamato Scientific Co., Ltd.)so as to have the composition in which the contents of Nd₂O₃, BaO, andTiO₂ were respectively 16.67 mol %, 15.67 mol %, and 67.66 mol %, andfired in the air at 900° C. for 10 hours to obtain a dielectricmaterial. Then the dielectric material was pulverized by a ball mill soas to have the mean particle size of 1.5 μm to obtain a dielectricceramics powder. To the dielectric ceramics powder, a 0.6 wt % PVA(polyvinyl alcohol) solution was added in the ratio of 10 wt %, and agranular powder was produced by use of a spray dryer.

[0151] Then, by using the apparatus shown in FIG. 1, the combustionflame 15 was generated while feeding LPG from the combustion gas feedingpipe 13 and oxygen from oxygen feeding pipe 14, and the above describedgranular powder was fed together with oxygen as the carrier gas into thecombustion flame 15. Incidentally, the flow rates of oxygen and LPG forgenerating the combustion flame 15, and the flow rate of oxygen as thecarrier gas were the same as in Example 1. For the powder thus obtained,the mean particle size was 2.276 μm, the 10% diameter was 0.97 μm, andthe 90% diameter was 5.56 μm. Namely, the ratio between the 10% diameterand the 90% diameter was only 5.7. In addition, the tap density was 5.76g/cm³, and the sphericity of the particles constituting the powderreached 0.93.

[0152] As a comparison example, the above described dielectric materialproduced, so as to have the composition in which the contents of Nd₂O₃,BaO, and TiO₂ were respectively 16.67 mol %, 15.67 mol %, and 67.66 mol%, was pulverized by use of a ball mill to obtain a pulverized powderwith the mean particle size of 1.757 μm (a dielectric ceramics powder).

[0153] Then, a resin was mixed in each of the spherical powder andpulverized powder to obtain composite dielectric material. Incidentally,the content of the dielectric ceramics powder in the compositedielectric material was made to be 40 vol % in both spherical powder andpulverized powder, and the resin used was a polyvinyl benzyl ethercompound represented by formula (1) in FIG. 7.

[0154] For the purpose of comparing the dispersion properties of thecomposite dielectric material based on the spherical powder (hereinafterreferred to as Sample 1) and the composite dielectric material based onthe pulverized powder (herein after referred to as Sample 2), thefollowing substrates were obtained as described below. Patterns wereformed by use of a glass fabric based epoxy resin, and the plates weremade of a copper foil coated respectively with Sample 1 and Sample 2.The substrates provided with the patterns and the plates were insertedin a press and press molding was performed under the conditionsspecified below to obtain substrates. Here, it should be noted that itwas difficult to fill the composite dielectric materials in the patternedges formed on the substrates. Accordingly, the fluidity was judged assatisfactory in the case where the composite dielectric material wasfilled in even near the pattern edges, while the fluidity was judged aspoor in the case where the composite dielectric material was not filledin near the pattern edges.

[0155] Press molding conditions:

[0156] Pressure: 40 kgf/cm²

[0157] Temperature: the temperature was increased from room temperatureup to 150° C., and maintained at that temperature for 30 min.Subsequently, the temperature was increased up to 195° C., andmaintained at that temperature for 3 hours.

[0158] Microscopic observation was performed on the sections of thesubstrate produced by using Sample 1 and the substrate produced by usingSample 2. The results obtained are shown in FIGS. 4 and 5. FIG. 5 showsschematically the sections shown in FIG. 4.

[0159] As shown in FIGS. 4(a) and 5(a), voids were confirmed to existnear the pattern edges in the case where the substrate was produced withSample 2. On the contrary, as shown in FIGS. 4(b) and 5(b), it wasconfirmed that the composite dielectric material was able to be denselyfilled in near the pattern edges in the case where Sample 1, namely, aspherical powder having a uniform particle size was used. From the aboveresults, it has been found that when a spherical powder is used, thefluidity of the composite dielectric material itself is improved ascompared to the case where a pulverized powder is used, and thecomposite dielectric material can be filled in without forming voids onthe substrate.

EXAMPLE 4

[0160] Description will be made, by referring to as Example 4, on anexperiment performed for the purpose of confirming the variations of thedielectric properties in a composite dielectric substance caused by thevariations in the filled-in amount of a dielectric ceramics powder.

[0161] The spherical dielectric ceramics powder obtained in Example 3was mixed in a polyvinyl benzyl ether compound represented by formula(1) to obtain Samples 3 to 5. The filled-in amounts of the sphericalpowder in Samples 3 to 5 were respectively 40 vol %, 45 vol %, and 50vol %. Boards were produced using Samples 3 to 5 in a manner similar tothat in Example 3, and the dielectric constant ε (2 GHz) was measuredfor each of the substrates produced by means of the cavity resonatormethod (a perturbation method) (the apparatus manufactured by HewlettPackard, Inc., 83260A and 8757C were used). Furthermore, the Q valueswere also obtained. The results thus obtained are shown in FIG. 6.Incidentally, for the convenience of comparison, there are also shownsimultaneously in FIG. 6 the dielectric constant ε and Q value of Sample2 produced in Example 3.

[0162] As shown in FIG. 6, Samples 3 to 5 all exhibited the dielectricconstants ε of 8 or above and the Q values of 300 or above, and hence ithas been confirmed that Samples 3 to 5 all have satisfactory dielectricproperties. In addition, as shown in FIG. 6, the dielectric propertiesare improved with increasing content of the dielectric ceramics powder,and it is noticed that when the content of the dielectric ceramicspowder becomes 45 vol % or above, the dielectric constant ε of 10 orabove is shown while still maintaining a high Q value of 350 or aboveeven at a high frequency of 2 GHz. A comparison between the dielectricproperties of Sample 3 (spherical powder) and that of Sample 2(pulverized powder) both containing the dielectric ceramics powder of 40vol % shows that Sample 2 shows a satisfactory dielectric constant ε,but the Q value thereof is 329 which is lower than the Q value of Sample3 (349) even by 20.

[0163] A microscopic examination of the section of Sample 5 gave aconfirmation that the spherical particles got into near the patternedges. Accordingly, it is expected that when a spherical powder having auniform particle size is used, the content of a dielectric ceramicspowder in a composite dielectric substance can be increased to 60 vol %or above, or furthermore, up to a value close to 70 vol %.

INDUSTRIAL APPLICATION

[0164] As described above in detail, according to the present invention,a granular powder is used as a material, and hence there can be obtaineda spherical oxide powder which is narrow in the width of the particlesize distribution. Moreover, according to the present invention, aspherical oxide powder is obtained by use of a combustion flame, andhence a cost reduction can be achieved as compared with the case where aspherical oxide powder is obtained by use of a plasma flame. Inaddition, according to the present invention, there can be obtained acomposite dielectric material and a substrate which are high indielectric constant ε and low in tan δ, and are suitable for use in theGHz high frequency band.

What is claimed is:
 1. A production method of spherical oxide powdercomprising: a feeding step in which a granular powder composed of anoxide composition is fed into a combustion flame together with a carriergas; a melting step in which said fed granular powder is melted in saidcombustion flame to obtain a melt; and a solidifying step in which saidmelt is solidified by being moved and placed outside said combustionflame.
 2. A production method of a spherical oxide powder according toclaim 1, wherein said granular powder is composed of the same oxide asin said spherical oxide powder obtained through said solidifying step.3. A production method of a spherical oxide powder according to claim 1,wherein said granular powder is composed of plural kinds of compoundparticles.
 4. A production method of a spherical oxide powder accordingto claim 1, wherein said spherical oxide powder obtained through saidsolidifying step is constituted by a dielectric material composed of acomposite oxide.
 5. A production method of a spherical oxide powderaccording to claim 1, wherein said spherical oxide powder obtainedthrough said solidifying step is 1 to 10 μm in mean particle size and0.9 or above in sphericity.
 6. A production method of a spherical oxidepowder wherein: producing a powder, in which two or more than two kindsof particles, capable of finally constituting a desired oxide powder bya thermal reaction, are aggregated in a state of being in contact witheach other; and making said powder produced to stay in a combustionflame for a prescribed period of time.
 7. A production method of aspherical oxide powder according to claim 6, wherein said oxide powderis constituted by allowing the particles composing said powder to reactwith each other in said combustion flame.
 8. A production apparatus ofspherical powder comprising: a burner for generating a combustion flame;an in-process substance feeding means for feeding a in-process substanceto said combustion flame; a chamber provided with an in-processsubstance transiting region through which said in-process substance,heat treated by said combustion flame, passes in a floating state; and aheating means for heating said in-process substance transiting region.9. A composite dielectric material comprising: a resin material; and aspherical dielectric powder which is dispersed in said resin materialand in which the sphericity is 0.82 to 1, and the ratio between the 10%diameter and the 90% diameter of the powder is 30 or below.
 10. Acomposite dielectric material according to claim 9, wherein saiddielectric powder is based on BaO—RO—TiO₂ (R: a rare earth element, RO:a rare earth oxide).
 11. A composite dielectric material according toclaim 9, wherein when the total content of said resin material and saiddielectric powder is represented as 100 vol %, the content of saiddielectric material is 30 vol % or above and smaller than 70 vol %. 12.A composite dielectric material according to claim 9, wherein saiddielectric powder is 0.5 to 10 μm in mean particle size.
 13. A compositedielectric material according to claim 9, wherein said dielectric powderis a spherical oxide powder produced by subjecting said dielectricpowder to a heat treatment for spheroidizing said dielectric powder. 14.A composite dielectric material according to claim 9, wherein said resinmaterial is a polyvinyl benzyl ether compound.
 15. A compositedielectric material according to claim 9, wherein said compositedielectric material has a higher Q value (Q=1/tan δ, tan δ being thedielectric dissipation factor) at 2 GHz than the Q value of said resinmaterial.
 16. A substrate in which a dielectric powder is dispersed in aresin material wherein: said dielectric powder is 30 or below in theratio between the 10% diameter and the 90% diameter and the sphericitythereof is 0.82 to
 1. 17. A production method of substrate comprising: astep of obtaining a spherical oxide powder in which the ratio betweenthe 10% diameter and the 90% diameter is 30 or below, the mean particlesize is 0.5 to 10 μm, and the sphericity thereof is 0.82 to 1, by usinga granular powder composed of an oxide composition; a step of obtaininga mixture by mixing said spherical oxide powder and a resin material inwhich when the total content of said resin material and said sphericaloxide powder is represented as 100 vol %, the content of said sphericaloxide powder is 30 vol % or above and smaller than 70 vol %; and a stepof obtaining a substrate by compressing said mixture.
 18. The productionmethod of substrate according to claim 17, whrein said spherical oxidepowder is a dielectric ceramics powder.